Hermetic reciprocating compressor with thrust ball bearing

ABSTRACT

A hermetic compressor includes a hermetic container that stores lubricating oil, an electrically-driven element having a stator and a rotor, a shaft having a compressing element driven by the electrically-driven element, and including an eccentric shaft portion, a cylinder block, a piston, a coupling device that connects the piston and the eccentric shaft portion, a main bearing, and a thrust ball bearing that supports a vertical load by the self weight of the rotor and the shaft. The thrust ball bearing includes a plurality of balls having a diameter of 3 mm or less, a holder portion holding the balls and formed of a polymeric material, and an upper washer and a lower washer disposed above and below the balls, respectively, and the viscosity grade of the lubricating oil is from ISO VG3 to ISO VG10.

TECHNICAL FIELD

The present invention relates to a hermetic compressor used for a refrigerating cycle of a freezing refrigerator, etc.

BACKGROUND ART

In recent years, as for a hermetic compressor used for a freezer of a freezing refrigerator, etc., attainment of high efficiency for reduction of power consumption is advanced. Conventionally, as a means for attaining the high efficiency of the hermetic compressor, a thrust ball bearing in which the sliding loss of a thrust bearing portion is reduced compared with a sliding bearing has been adopted. Meanwhile, lowering of viscosity of lubricating oil is advanced in order to reduce the sliding loss.

As this type of conventional hermetic compressor, there is one in which upper and lower portions of a ball is sandwiched by a washer, and a thrust ball bearing of an inexpensive and simple configuration using a cage made of a polymeric material is used to attain high efficiency (for example, refer to Patent Document 1).

Hereinafter, the conventional hermetic compressor will be explained with reference to drawings.

FIG. 5 is a longitudinal sectional view of the conventional hermetic compressor described in Patent Document 1, and FIG. 6 is an exploded perspective view of chief portions of the hermetic compressor.

As shown in FIG. 5, electrically-driven element 4 provided with stator 2 and rotor 3, and compressing element 5 driven by electrically-driven element 4 are accommodated within hermetic container 1, and lubricating oil 6 is stored within hermetic container 1.

Shaft 10 has main shaft portion 11 to which rotor 3 is fixed, and eccentric shaft portion 12 formed eccentrically from the main shaft portion 11.

Cylinder block 14 has substantially cylindrical compression chamber 15, and main bearing 20. Piston 23 is reciprocally and slidably inserted into compression chamber 15 of cylinder block 14, and is connected to eccentric shaft portion 12 by coupling device 24 and piston pin 25.

Annular upper washer seating surface 27 is formed approximately perpendicularly to the shaft center of main shaft portion 11, on the side of main shaft portion 11 between main shaft portion 11 and eccentric shaft portion 12 of shaft 10. Further, annular lower washer seating surface 28 is formed approximately perpendicularly to the shaft center of main bearing 20, at the upper end of main bearing 20.

Thrust ball bearing 29 is provided between upper washer seating surface 27 and the lower washer seating surface 28 to support the load of shaft 10 and rotor 3 in the direction of gravity.

As shown in FIG. 6, thrust ball bearing 29 is composed of a plurality of balls 30, cage 31 that is formed of a polymeric material represented by nylon, and holds balls 30, and upper washer 32 and lower washer 33 that are respectively disposed above and below balls 30. Upper washer 32 and lower washer 33 are formed from a flat plate made of quenched iron.

The operation of the hermetic compressor configured as described above will be explained below.

Rotor 3 of electrically-driven element 4 rotates shaft 10, and the rotational motion of eccentric shaft portion 12 is transmitted to piston 23 via coupling device 24, whereby piston 23 reciprocates in compression chamber 15. Thereby, after refrigerant gas is sucked and compressed into compression chamber 15 from a cooling system that is not shown, the gas is discharged again to the cooling system.

The weight of shaft 10 and rotor 3 is supported by thrust ball bearing 29. At the time of rotation of shaft 10, balls 30 roll between upper washer 32 and lower washer 33. Therefore, shaft 10 rotates smoothly.

At the time of rotation of shaft 10, upper washer 32 is brought into close contact with upper washer seating surface 27, and lower washer 33 is brought into close contact with the lower washer seating surface 28. Further, cage 31 holds balls 30 so that balls 30 may not jump out by a centrifugal force.

Since the torque that rotates shaft 10 by using thrust ball bearing 29 becomes small compared with the thrust sliding bearing, the loss in the thrust bearing can be made small. Accordingly, the input to the hermetic compressor can be reduced to attain high efficiency.

However, in the conventional configuration, there is a problem that cage 31 may worn out and reliability may be lowered, in a case where lubricating oil 6 of low viscosity grade like ISO VG3 to ISO VG10 is used.

Patent Document 1: Japanese Unexamined Patent Publication No. 2005-127305 DISCLOSURE OF THE INVENTION

The present invention provides a hermetic compressor including: a hermetic container that stores lubricating oil; an electrically-driven element including a stator and a rotor; a shaft having a compressing element driven by the electrically-driven element, and including a main shaft to which the rotor is fixed, and an eccentric shaft portion formed via a flange portion; a cylinder block including a cylindrical compression chamber; a piston that reciprocates within the compression chamber; a coupling device that connects the piston and the eccentric shaft portion; a main bearing that is formed in the cylinder block to journal the main shaft portion of the shaft; and a thrust ball bearing that supports a vertical load by the self-weight of the rotor and the shaft. The thrust ball bearing includes a plurality of balls having a diameter of 3 mm or less, a holder portion holding the balls and formed of a polymeric material, and an upper washer and a lower washer disposed above and below the balls, respectively, and the viscosity grade of the lubricating oil is from ISO VG3 to ISO VG10.

According to the hermetic compressor having such a configuration, the balls are made light to reduce the centrifugal force, consequently to reduce the surface pressure applied to the holder portion. By using the holder portion under a surface pressure lower than a sliding limit of a polymeric material, the effect of reducing the sliding loss of a thrust bearing portion can be maintained, the wear of holder portion can be prevented even if the high efficiency is attained using a lubricating oil of low viscosity. As a result, a hermetic compressor that is highly efficient and highly reliable can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a hermetic compressor in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a sectional view of a chief portion of the hermetic compressor in accordance with the exemplary embodiment of the present invention;

FIG. 3 is an enlarged sectional view of a chief portion of a thrust ball bearing of the hermetic compressor in accordance with the exemplary embodiment of the present invention;

FIG. 4 is a graph showing characteristics of PV values in a holder portion of the hermetic compressor in accordance with the exemplary embodiment of the present invention;

FIG. 5 is a longitudinal sectional view of a conventional hermetic compressor; and

FIG. 6 is an exploded perspective view of a chief portion of the conventional hermetic compressor.

REFERENCE NUMERALS

-   100: HERMETIC COMPRESSOR -   101: HERMETIC CONTAINER -   102: LUBRICATING OIL -   103: STATOR -   104: ROTOR -   105: ELECTRICALLY-DRIVEN ELEMENT -   106: COMPRESSING ELEMENT -   110: SHAFT -   111: MAIN SHAFT PORTION -   112: FLANGE PORTION -   113: ECCENTRIC SHAFT PORTION -   120: CYLINDER BLOCK -   121: COMPRESSION CHAMBER -   122: MAIN BEARING -   130: PISTON -   131: COUPLING DEVICE -   140: THRUST BALL BEARING -   141: UPPER END SURFACE -   142: BALL -   143: HOLDER PORTION -   144: UPPER WASHER -   145: LOWER WASHER -   150: POCKET PORTION -   151: INNER SURFACE -   152: UPPER PORTION -   153: OIL SUPPLY PASSAGE

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be explained with reference to the drawings. In addition, the present invention is not limited by the embodiment. (Embodiment)

FIG. 1 is a longitudinal sectional view of a hermetic compressor of the embodiment of the present invention.

Hermetic compressor 100 stores lubricating oil 102 in hermetic container 101, and electrically-driven element 105 provided with stator 103 and rotor 104, and compressing element 106 that is driven by electrically-driven element 105 and is disposed above electrically-driven element 105 are accommodated.

Shaft 110 constituting compressing element 106 has main shaft portion 111 into which rotor 104 is fixedly shrinkage-fitted, and eccentric shaft portion 113 formed eccentrically from main shaft portion 111 via flange portion 112. Further, oil supply mechanism 114 is formed inside shaft 110.

Cylinder block 120 has substantially cylindrical compression chamber 121, and is formed with main bearing 122 that journals main shaft portion 111 of shaft 110. Piston 130 is reciprocally and slidably inserted into compression chamber 121 of cylinder block 120, and is connected to eccentric shaft portion 113 by coupling device 131 and piston pin 132. Here, piston 130 reciprocates within compression chamber 121.

Thrust ball bearing 140 is disposed between flange portion 112 and upper end surface 141 of main bearing 122 to support a vertical load generated by the self-weight of rotor 104 and shaft 110.

FIG. 2 is a sectional view of chief portions of the hermetic compressor of the embodiment of the present invention. Thrust ball bearing 140 includes a plurality of balls 142 having a diameter of 3 mm or less. Balls 142 of the hermetic compressor of the embodiment of the present invention have a diameter of 2.0 mm, and the number thereof is 14.

Thrust ball bearing 140 includes holder portion 143 that is formed of nylon 66 of a polymeric material and holds balls 142, and upper washer 144 and lower washer 145 that are respectively disposed above and below balls 142. In addition, upper washer 144 and lower washer 145 are flat plates that are made of iron and that are subjected to annular quenching.

Holder portion 143 is formed annularly, and includes a plurality of pocket portions 150 that hold balls 142 disposed at regular intervals along the raceway circumference of balls 142. In addition, the raceway diameter d of balls 142 shown in FIG. 2 is 23 mm.

FIG. 3 is an enlarged sectional view of chief portions of the thrust ball bearing of the embodiment of the present invention. Inner surface 151 of pocket portion 150 has the radius of curvature R2 that is less than the radius of curvature R1 of balls 142, and the balls 142 and the holder portion 143 come into annular line contact with each other at the edges of the pocket portions 150. Specifically, R2 is set to 0.9 mm or more and less than 1 mm so as to be slightly smaller than 1 mm that is the radius of curvature R1 of balls 142.

Therefore, a slight gap is formed between balls 142 and pocket portion 150.

Furthermore, holder portion 143 is provided with oil supply passage 153 that allows upper portion 152 of holder portion 143 and inner surface 151 of pocket portion 150 in the vicinity where balls 142 approaches to communicate with each other directly in the vertical direction.

Electrically-driven element 105 is of a concentrated winding type in which a winding line is wound in a concentrated manner around a teeth portion provided in the core of stator 103. Further, electrically-driven element 105 is driven with a plurality of operation frequencies by inverter control. Specifically, the rotor 104 can perform operation with a rotational frequency of at least 60 Hz or more, and the maximum rotational frequency is 80 Hz.

Refrigerant used for the hermetic compressor of the embodiment of the present invention is a hydrocarbon-based refrigerant that is a natural refrigerant that has a low warming potential, and is represented by R134a or R600a whose ozone depletion potential is zero. The refrigerant is combined with lubricating oil with high compatibility. Lubricating oil 102 to be used has a viscosity grade of ISO VG3 to ISO VG10, and is lubricating oil with low viscosity.

The operation of the hermetic compressor configured as described above will be explained below.

Rotor 104 of electrically-driven element 105 rotates shaft 110, and the rotational motion of eccentric shaft portion 113 is transmitted to piston 130 via coupling device 131. Piston 130 reciprocates within compression chamber 121. Thereby, after refrigerant gas is sucked and compressed into compression chamber 121 from a cooling system that is not shown, the gas is discharged again to the cooling system.

At this time, when shaft 110 rotates, balls 142 make an orbital motion about the shaft center of shaft 110 by the rotational frequency of almost half of the rotational frequency of shaft 110. For this reason, the radial outward centrifugal force of shaft 110 acts on balls 142.

This centrifugal force is obtained by multiplying the mass of balls 142, the raceway radius of balls 142, and the square of angular velocity. Accordingly, surface pressure P that acts on pocket portion 150 by the centrifugal force that acts on balls 142 is obtained by dividing this centrifugal force by a contact area. Further, sliding speed V is obtained depending on the rotational speed of balls 142. PV value that is obtained by multiplying surface pressure P by sliding speed V is known as an important index for prevention of seizure.

On the other hand, the sliding limit where a polymeric material does not cause seizure is described in catalog of material makers, scientific papers, etc. as a limiting PV value. It is reported that the limiting PV value of nylon 66 is about 0.18 MPa·m/s, and that the limiting PV value of nylon 46 is about 0.3 MPa·m/s. In order for holder portion 143 not to cause seizure, the PV value of holder portion 143 needs to be a value smaller than the above limiting PV value.

FIG. 4 is a graph showing characteristics of PV values in the holder portion of the hermetic compressor of the embodiment of the present invention.

In FIG. 4, PV values are shown on the axis of ordinate, ball diameters are shown on the axis of abscissa, and the ball diameters are set as parameters. In a case where the raceway diameter of balls 142 23 mm, and driving is made at a commercial power frequency of 60 Hz, PV values that are calculated theoretically are represented by a solid line and a dotted line.

The solid line shows the characteristics of the PV values in a case where the radius of curvature of pocket portion 150 of holder portion 143 is beyond the radius of curvature of balls, and pocket portion 150 and balls 142 are in a sliding state of point contact.

The dotted line shows the hermetic compressor of the embodiment of the present invention, and shows the characteristics of PV values in a case where the radius of curvature of pocket portion 150 of holder portion 143 is smaller than the radius of curvature of balls 142, and pocket portion 150 and balls 142 are in a sliding state of annular line contact.

In FIG. 4, the limiting PV value of the nylon 66 that is a material of holder portion 143, and the limiting PV value of nylon 46 are shown by broken lines.

In balls with a diameter of 3.17 mm that is used conventionally, its PV value is estimated at about 0.19 MPa·m/s (black dot in FIG. 4), and is estimated to be almost the same as the limiting PV value of nylon 66.

Accordingly, the sliding state of slip sliding between the balls and holder portion 143 become severe, and an oil film is broken.

This results in a boundary lubrication state, and it is inferred that the possibility that seizure occurs between the balls and holder portion 143 is high.

In addition, in a case where nylon 46 is used for holder portion 143, its limiting PV value becomes high compared with nylon 66. Thus, the reliability of the sliding portions between the balls and holder portion 143 improves. However, nylon 46 is expensive compared with nylon 66.

On the other hand, when the PV value of the hermetic compressor of the embodiment of the present invention is calculated, the value is estimated to be 0.08 or less MPa·m/s (white circle in FIG. 4), and even if nylon 66 is used for holder portion 143, a sliding state below a limiting PV value is obtained.

This has two factors.

First, a PV value can be lowered by setting the diameter of balls 142 to a small value of 2 mm to reduce the weight of the balls, and by reducing the centrifugal force that acts on balls 142, to reduce the surface pressure applied to holder portion 143.

Second, the radius of curvature of pocket portion 150 of holder portion 143 is made smaller than the radius of curvature of balls 142. Therefore, pocket portion 150 and balls 142 will be in a sliding state of annular line contact instead of a sliding state of point contact, and thus a contact portion is widened. As a result, the surface pressure P that acts on holder portion 143 can be reduced, and the PV value can be lowered. These two factors are differences between the solid line and the dotted line shown in FIG. 4.

As described above, in the hermetic compressor of the embodiment of the present invention, balls 142 are made light to reduce the centrifugal force, and the surface pressure applied to holder portion 143 is reduced. Moreover, the radius of curvature of pocket portion 150 of holder portion 143 is made smaller than the radius of curvature of balls 142 so that pocket portion 150 and balls 142 may be in a sliding state of annular line contact. As a result, while the effect of reducing the sliding loss of a thrust bearing portion can be maintained, the wear of holder portion 143 can be prevented even if high efficiency is attained using lubricating oil 102 of low viscosity.

In addition, in the hermetic compressor of the embodiment of the present invention, nylon 66 is used for holder portion 143. However, as clear from FIG. 4, the limiting PV value becomes still higher in a case where nylon 46 is used for holder portion 143. Therefore, although cost becomes high, a more reliable sliding state can be obtained.

Further, oil supply passage 153 that allows upper portion 152 of holder portion 143 with inner surface 151 of pocket portion 150 to communicate with each other directly is provided. Therefore, lubricating oil 102 supplied by oil supply mechanism 114 is supplied to a sliding place between balls 142 and pocket portion 150, so that an oil film can be formed, and reliability can be made higher.

Further, at the time of compression, piston 130 receives a large load accompanying the compression of a refrigerant, and receives the load that is distributed in the vicinity of upper and lower ends of main bearing 122, through eccentric shaft portion 113 of shaft 110 and main shaft portion 111 of shaft 110, via coupling device 131.

Accordingly, the moment that has eccentric shaft portion 113 as a force point, and has the vicinities of the upper and lower ends of main bearing 122 as a fulcrum acts on shaft 110, and a load acts on thrust ball bearing 140 via main bearing 122 and flange portion 112.

Further, in the hermetic compressor of the embodiment of the present invention, balls 142 are made to have a small diameter. Thus, the force point and the fulcrum are brought close to each other. Therefore, the moment that acts on shaft 110 can be reduced, the load applied to main bearing 122 can be reduced, and the sliding loss can be reduced. Also, since an uneven load component that is caused by the compression of a refrigerant and applied to thrust ball bearing 140 can be reduced, reliability and efficiency can be further improved.

Further, electrically-driven element 105 is driven at a plurality of operation frequencies by an inverter. As for the PV value at the time of operation of 80 Hz that is a maximum rotational frequency where the centrifugal force applied to balls 142 is large, the PV value of the conventional balls with a diameter of 3.17 mm becomes about 0.44 MPa·m/s, and exceeds the limiting PV value of nylon 46. However, it is estimated that the PV value of the hermetic compressor of the embodiment of the present invention becomes only about 0.18 MPa-m/s or less, and can be made below the limiting PV value of nylon 46. Accordingly, even if rotor 104 rotates at a rotational frequency 60 Hz or more where the centrifugal force becomes large, the wear of holder portion 143 formed of a polymeric material is reduced, and the effect of enhancing the reliability becomes remarkable. As a result, since this prevents balls 142 and holder portion 143 from seizing, and particularly, functions effectively to keep a good sliding state, reliability can be further enhanced.

In addition, balls 142 are made of a bearing steel material. However, in a case where ceramic or the like having small density is used, the centrifugal force applied to balls 142 can be further reduced, and the sliding state of balls 142 and holder portion 143 can be kept well.

INDUSTRIAL APPLICABILITY

As described above, since the hermetic compressor of the present invention can maintain the effect of reducing the sliding loss of a thrust bearing portion, and can prevent the wear of the holder portion, it can be applied to hermetic compressors of an air conditioner or a freezing and refrigerating apparatus. 

1. A hermetic compressor comprising: a hermetic container that stores lubricating oil; an electrically-driven element including a stator and a rotor; a shaft having a compressing element driven by the electrically-driven element, and including a main shaft, to which the rotor is fixed, and an eccentric shaft portion formed via a flange portion; a cylinder block including a cylindrical compression chamber; a piston that reciprocates within the compression chamber; a coupling device that connects the piston and the eccentric shaft portion; a main bearing that is formed at the cylinder block to journal the main shaft portion of the shaft; and a thrust ball bearing that supports a vertical load by self-weight of the rotor and the shaft, wherein the thrust ball bearing includes a plurality of balls having a diameter of 3 mm or less, a holder portion holding the balls and formed of a polymeric material, and an upper washer and a lower washer disposed above and below the balls, respectively, and viscosity grade of the lubricating oil is from ISO VG3 to ISO VG10.
 2. The hermetic compressor of claim 1, wherein the holder portions is provided with a plurality of pocket portions holding the balls, an inner surface of the pocket portion is formed so as to have a radius of curvature that is less than a radius of curvature of the ball, and the ball and the holder portion come into annular line contact with each other at the edge of the pocket portion.
 3. The hermetic compressor of claim 1, further comprising: an oil supply passage that allows an upper portion of the holder portion and an inner surface of the pocket portion to directly communicate with each other.
 4. The hermetic compressor of claim 1, wherein the compressing element is disposed above the electrically-driven element, and the thrust ball bearing is disposed between the flange portion and an upper end surface of the main bearing.
 5. The hermetic compressor of claim 1, wherein the electrically-driven element is driven at a plurality of operation frequencies by an inverter, and the rotor rotates at a rotational frequency of at least 60 Hz or more. 